CODEWITHSUNDEEP
javagenericswildcard
Attila Neparáczki
Attila Neparáczki

Reputation: 476

method return type from a class variable

Given the following class:

  ...

  Class<? extends Enum<?>> enumType;

  public MyClass(Class<? extends Enum<?>> enumType) {
    super();

    this.enumType=enumType;

  ...

How do i define a method that returns an Enum of the "enumType" class?

I need something like:

public enumType getValue(){
  ...
}

,but this doesn't work ..

Upvotes: 0

Views: 93

Answers (2)

Jesper
Jesper

Reputation: 206996

Use a type parameter instead of a wildcard. For example:

class MyClass<T extends Enum<T>> {
    private Class<T> enumType;

    public MyClass(Class<T> enumType) {
        this.enumType = enumType;
    }

    public T getValue() {
        // ...
    }
}

edit In response to your comment, here's a method that lists all constants of an arbitrary enum:

public <E extends Enum<E>> void showEnumValues(Class<E> e) {
    for (E value : e.getEnumConstants())
        System.out.println(value);
    }
}

Upvotes: 7

chrylis -cautiouslyoptimistic-
chrylis -cautiouslyoptimistic-

Reputation: 77226

You have to actually specify a variable inside your generic, not just use wildcards everywhere. Then it's just like this:

public class MyClass<E extends EnumType<E>> {
    Class<E> enumType;
    E value;

    public MyClass(Class<E> enumType) {
        this.enumType = enumType;
    }

    public E getValue() {
        return value;
    }
}

Upvotes: 3

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